T-568B Colour Code for RJ-45 Plug

Eight-conductor data cable contains 4 pairs of wires. The pairs are twisted together. To maintain reliability on Ethernet, you should not untwist them any more than necessary (max of about 1 cm).

Open end of connector here

There are two wiring standards for these cables, called "T-568A" and T-568B" They differ only in connection sequence, not in use of the various colours. The illustration shown is for T-568B. The pairs designated for 10BaseT Ethernet are Orange and Green. The other two pairs, Brown and Blue, can be used for a second Ethernet line or for phone connections.

Note that the Blue pair is on the centre pins and conveniently corresponds to the Red and Green pair in a normal phone line. The connections shown are specifically for an RJ45 plug (the thing on the end of the wire). The wall jack may be wired in a different sequence because the wires are actually crossed inside the jack. The jack should either come with a wiring diagram or at least designate pin numbers that you can match up to the colour code below.